Musnad Abu Ya'la al-Mawsili 151:49

Abu Bakr ibn Abi Shaybah narrated to us, Yazid ibn Harun narrated to us, al-Mas'udi informed us, from Simak ibn Harb, from 'Abd al-Rahman ibn 'Abd Allah, from his father, 'Abd Allah: That two men were worshipping Allah, and they asked Allah to cause them both to die together, so they died together and were buried. 'Abd Allah said: If I were there, I would have shown you their graves with the description that the Messenger of Allah (may Allah bless him and grant him peace) described to us.